Title: Stable cosmological solutions in extended vector-tensor theory

Abstract :
Many cosmological observations imply the existence of dark matter and
dark energy which induces the current accelerated expansion of the
universe. As a possible origin of such dark energy, scalar-tensor
theories draw much attention where scalar field is introduced as a
driving force for the accelerated expansion of the universe. Recently
there has been growing interest in degenerate theories to uncover yet
new theories of scalar field. After explaining the idea of degenerate
kinetic matrix, we will introduce our work where this notion was
applied to the theory of vector field for the first time. And then we
will discuss application to cosmology of this theory founding stable
solutions for cosmological perturbations which is in sharp contrast to
the case of degenerate scalar-tensor theory.